Surface-coated cutting tool

ABSTRACT

This invention provides a surface-coated cutting tool which exhibits excellent fracture resistance and wear resistance in high-speed cutting, such as high-speed gear cutting, high-speed milling, and high-speed drilling. The surface-coated cutting tool includes a hard coating layer composed of an alternately laminated layer structure of at least a thin layer A and a thin layer B formed on the surface of a tool substrate, such as a cemented carbide substrate, a cermet substrate, and a high-speed tool steel substrate. The thin layer A is an (Al, Cr, Si)N layer which satisfies a compositional formula: [Al X Cr Y Si Z ]N (0.2≦X≦0.45, 0.4≦Y≦0.75, 0.01≦Z≦0.2, and X+Y+Z=1 in terms of atomic ratio). The thin layer B is an (Al, Ti, Si)N layer which satisfies a compositional formula: [Al U Ti V Si W ]N (0.05≦U≦0.75, 0.15≦V≦0.94, 0.01≦W≦0.1, and U+V+W=1 in terms of atomic ratio).

This application is a reissue application of U.S. Pat. No. 8,354,177,granted Jan. 15, 2013 which claims the right of priority under 35 U.S.C.§119 based on Japanese Patent Application No. 2007-209323 filed Aug. 10,2007.

TECHNICAL FIELD

The present invention relates to a surface-coated cutting tool(hereinafter referred to as a coated tool) in which a hard coating layerhas excellent high-temperature hardness, high-temperature toughness,high-temperature strength, and thermoplastic deformation resistance.

This hard coating layer has excellent fracture resistance and wearresistance, and exhibits excellent tool performance for a prolongedperiod of time; even when being used for cutting processes, for example,high-speed gear cutting, high-speed milling, and high-speed drilling, inwhich high temperature is generated, and also a large impact andmechanical load is applied to a cutting edge.

BACKGROUND ART

As the coated tools, the tools;

-   an insert, which is detachably attached to a edge portion of a    holder, used for turning or planing various workpieces made of steel    and/or cast iron;-   a drill and a Printed Circuit Board drill used for drilling the    workpieces;-   an end mill used for face milling, slotting and shoulder milling the    workpieces; and-   a solid hob cutter and a shaper cutter used for gear cutting a tooth    profile of the workpieces;    are generally known.

Further, a coated tool: wherein

-   its tool substrate, namely, tool body, is made of, for example,    -   a tungsten-carbide (hereinafter shown by WC) based cemented        carbide,    -   a titan-carbonitride (hereinafter shown by TiCN) based cermet,        or    -   a high-speed tool steel (hereinafter referred to as high-speed        steel);-   to improve its thermal resistance and wear resistance, at least one    or more layers of hard coating layers composed of a complex nitride    layer of Al, Cr, and Si (hereinafter shown by an (Al, Cr, Si)N    layer) are provided on the surface of the tool substrate; and-   when expressing a composition of the complex nitride layer as a    compositional formula [Al_(X)Cr_(Y)Si_(X)]N, each X, Y and Z    satisfies the relations,    0.75≦X≦0.95, 0.05≦Y≦0.25, and X+Y+Z=1-    (where all of X, Y, and Z are atomic ratios);    is specifically known.

Also, a coated tool: wherein

-   to improve its oxidation resistance and wear resistance, at lease    one or more of hard coating layers composed of a complex nitride    layer of Al, Ti, and Si (hereinafter shown by an (Al, Ti, Si)N    layer) are provided on the surface of the tool substrate; and-   when expressing a composition of the complex nitride layer as a    compositional formula [Al_(U)Ti_(V)Si_(W)]N,    -   each U, V and W satisfies the relations,        0.05≦U≦0.75, 0.01≦W≦0.10, and U+V+W=1    -   (where all of U, V, and W are atomic ratios);        is known.

Further, a process for manufacturing, the above conventional coated toolis known.

This process is:

-   -   the above tool substrate is placed into an arc ion plating        apparatus that is one type of a physical vapor deposition        apparatus, for example, shown in the schematic explanatory view        of FIG. 2:    -   under a condition that the inside of the apparatus is heated up        to a temperature of 500° C. for example, arc discharge between a        cathode (evaporation source) and an anode is generated with an        electric current of 90 A for example, wherein the cathode has a        component composition according to the type of hard coating        layer to be vapor-deposited and formed on the tool substrate:    -   simultaneously, a nitrogen gas, which is a reaction gas, is        introduced into the apparatus to create a reaction atmosphere of        2 Pa:    -   further, a bias voltage of −100 V, for example, is applied to        the above tool substrate:    -   the above hard coating layer is formed on the surface of the        tool substrate.

-   [Patent Document 1] Japanese Unexamined Patent Application    Publication No. 2006-175569

-   [Patent Document 2] Japanese Patent No. 2793773

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

In recent years, the performance of machine tools for cutting has beenremarkably enhanced, and demand for labor-saving and energy-saving incutting process and cost reduction has increased.

Accordingly, the cutting process tends to be carried out at a higherspeed increasingly. The above conventional coated tools encounter noparticular problems when being used in cutting process for steel, castiron, etc. under normal cutting conditions. However, when theseconventional coated tools are used for cutting processes, for example,high-speed gear cutting, high-speed milling, and high-speed drilling, inwhich high temperature is generated, and a large impact and mechanicalload is applied to a cutting edge; the tool life of these tools is notso long period.

The insufficient toughness of the hard coating layer, the occurrence ofpartial wear caused by thermoplastic deformation, and/or the like, makethe occurrence of chipping and/or fractures uncontrolled; and alsoprogress of wear is accelerated. Therefore, the tool life of these toolsbecomes shortened comparatively.

Means for Solving the Problems

Thus, the present inventors have obtained the following knowledge fromthe above-described viewpoints as a result of paying attention to andstudying a layer forming material which constitutes the hard coatinglayers of the above conventional coated tools, and its structure inorder to develop a coated tool in which the hard coating layer exhibitsexcellent fracture resistance and wear resistance under cuttingconditions, such as high-speed gear cutting, high-speed milling, andhigh-speed drilling, in which high temperature is generated, and a largeimpact and mechanical load is applied to a cutting edge.

(a) The Al component in the (Al, Cr, Si)N layer which constitutes thehard coating layer of the above conventional coated tool (refer toPatent Document 1) has an effect of improving high-temperature hardness.The Cr component in the (Al, Cr, Si)N layer has an effect of improvinghigh-temperature toughness and high-temperature strength. Both Al and Crcomponents in the (Al, Cr, Si)N layer have an effect of improvinghigh-temperature oxidation resistance in a state of coexisting with eachother. Further, Si component in the (Al, Cr, Si)N layer has an effect ofimproving thermoplastic deformation resistance.

However, the above high-temperature toughness and high-temperaturestrength are not sufficient for severe cutting conditions, such ashigh-speed gear cutting, high-speed milling, and high-speed drilling, inwhich high temperature is generated, and also a large impact andmechanical load is applied to a cutting edge. Therefore, this problemcauses chipping, fractures, and etc.

If an attempt, in which a Cr content ratio is increased for improvinghigh-temperature toughness and high-temperature strength, is carriedout; this attempt also makes the Al content ratio decreased relatively,and then the wear resistance deteriorates. Therefore, there is a limitto the suppression and improvement of the chipping resistance andfracture resistance in the hard coating layer composed of the (Al, Cr,Si)N layer.

(b) On the other hand, the Al component and Si component in the (Al, Ti,Si)N layer which constitutes the hard coating layer of the aboveconventional coated tool (refer to Patent Document 2) has the sameeffects as described above.

Also the Ti component in the (Al, Ti, Si)N layer has an effect offurther improving high-temperature toughness and high-temperaturestrength.

Therefore, the hard coating layer composed of the (Al, Ti, Si)N layerexhibits excellent chipping resistance and fracture resistance undersevere cutting conditions, such as the high-speed gear cutting,high-speed milling, and high-speed drilling. However, since thehigh-temperature hardness and thermoplastic deformation resistance areinsufficient, the wear resistance is poor.

(c) Thus, an attempt to form a hard coating layer; which has analternately laminated layer structure of

-   -   thin layer A composed of the (Al, Cr, Si)N layer of the        above (a) with a predetermined composition and a predetermined        thickness, and    -   thin layer B composed of the (Al, Ti, Si)N layer of the        above (b) with a predetermined composition and a predetermined        thickness;        was carried out.

Each thin layer A and thin layer B, which compose the alternatelylaminated layer structure of the hard coating layer, has eachcomposition in a predetermined range, and has each thickness in apredetermined range.

Thereby, the hard coating layer can have the excellent wear resistanceof the thin layer A and the excellent high-temperature toughness andhigh-temperature strength of the thin layer B as the whole hard coatinglayer.

Therefore, the coated tool, on which the hard coating layer having astructure in alternately laminated layer of the thin layers A and B isformed, can exhibit excellent chipping resistance, fracture resistance,and wear resistance; even when this coated tool is used for cuttingprocess under severe cutting conditions, such as high-speed gearcutting, high-speed milling, and high-speed drilling, in which hightemperature is generated, and a large impact and mechanical load isapplied to a cutting edge.

The invention was made on the basis of the above knowledge.

(1) In a surface-coated cutting tool (coated tool) comprising a hardcoating layer formed on the surface of a tool substrate,

-   the hard coating layer is composed of an alternately laminated layer    structure of at least a thin layer A and a thin layer B; and-   the thin layer A has a thickness of 0.01 to 0.1 μm,-   the thin layer B has a thickness of 0.01 to 0.1 μm, and-   a total thickness of the thin layers A and B is within 1 to 10 μm:    wherein-   (a) the thin layer A is a complex nitride layer of Al, Cr and Si    ((Al, Cr and Si)N layer), and when expressing a composition of the    complex nitride layer as a compositional formula    [Al_(X)Cr_(Y)Si_(Z)]N,    -   each X, Y and Z satisfies the relations,        0.2≦X≦0.45, 0.4≦Y≦0.75, 0.01≦Z≦0.2, and X+Y+Z=1    -   (where all of X, Y, and Z are atomic ratios); and        (b) the thin layer B is a complex nitride layer of Al, Ti, and        Si ((Al, Ti and SON layer), and when expressing a composition of        the complex nitride layer as a compositional formula        [Al_(U)Ti_(V)Si_(W)]N,    -   each U, V and W satisfies the relations,        0.05≦U≦0.75, 0.15≦V≦0.94, 0.01≦W≦0.1, and U+V+W=1    -   (where all of U, V, and W are atomic ratios).        (2) In the surface-coated cutting tool (coated tool) described        in the above (1), its hard coating layer includes    -   an upper layer composed of an alternately laminated layer        structure of the thin layer A and the thin layer B, and    -   a under layer formed so as to be interposed between the upper        layer and the surface of the tool substrate;        wherein    -   the under layer has a thickness of 0.5 to 10 μm, and has a        composition which satisfies the compositional formula of the        thin layer A.        (3) In the surface-coated cutting tool (coated tool) described        in the above (1), its hard coating layer includes    -   an upper layer having an alternately laminated layer structure        of the thin layer A and the thin layer B, and    -   a under layer formed so as to be interposed between the upper        layer and the surface of a tool substrate;        wherein    -   the under layer has a thickness of 0.5 to 10 μm, and has a        composition which satisfies the compositional formula of the        thin layer B.        (4) A surface-coated cutting tool (coated tool) according to the        surface-coated cutting tool (coated tool) described in any one        of the above (1) to (3) is a gear cutter in which its tool        substrate, namely body, is made of a high-speed tool steel.        (5) A surface-coated cutting tool (coated tool) according to the        surface-coated cutting tool (coated tool) described in any one        of the above (1) to (3) is an end mill in which its tool        substrate, namely body, is made of a high-speed tool steel.        (6) A surface-coated cutting tool (coated tool) according to the        surface-coated cutting tool (coated tool) described in any one        of the above (1) to (3) is an end mill or a drill in which its        tool substrate, namely body, is made of a tungsten-carbide-based        cemented carbide.

Next, the reasons for limiting numerical values as described aboveregarding the hard coating layer of the coated tool of the inventionwill be described below.

(a) Thin Layer A

The Al component in the thin layer A composed of the (Al, Cr, SON layerhas an effect of improving high-temperature hardness. The Cr componentin the thin layer A composed of the (Al, Cr, Si)N layer has an effect ofimproving high-temperature toughness and high-temperature strength. TheAl and Cr components in the thin layer A composed of the (Al, Cr, Si)Nlayer have an effect of improving high-temperature oxidation resistancein a state of coexisting with each other.

Further, the Si component in the thin layer A composed of the (Al, Cr,Si)N layer has an effect of improving thermoplastic deformationresistance.

If the X value (atomic ratio) indicating the content ratio of Al to thetotal content including Cr and Si, is less than 0.2; minimumhigh-temperature hardness and high-temperature oxidation resistancecannot be achieved, and such X value causes acceleration of wear.

On the other hand, if the X value exceeds 0.45; high-temperaturetoughness and high-temperature strength decreases, and also such X valuecauses occurrence of chipping or fractures.

Therefore, the X value was determined in the range of 0.2 to 0.45.

Additionally, if the Y value (atomic ratio) indicating the content ratioof Cr to the total content including Al and Si, is less than 0.4; therequired minimum high-temperature toughness and high-temperaturestrength cannot be achieved, and also the occurrence of chipping orfractures becomes uncontrolled.

On the other hand, if the Y value exceeds 0.75; the content ratio of Aldecreases relatively, and also such Y value accelerates the progress ofwear.

Therefore, the Y value was determined in the range of 0.4 to 0.75.Moreover, if the Z value (atomic ratio) indicating the content ratio ofSi to the total content including Al and Cr, is less than 0.01; theimprovement of wear resistance accompanied by the improvement ofthermoplastic deformation resistance cannot be expected.

On the other hand, if the Z value exceeds 0.2; the wear-resistanceimproving effect shows a tendency to decrease. Therefore, the Z valuewas determined in the range of 0.01 to 0.2.

In addition, especially preferable ranges regarding the above X, Y, andZ are 0.35≦X≦0.45, 0.4≦Y≦0.55, and 0.03≦X≦0.10 respectively.

(b) Thin Layer B

The thin layer B is composed of the (Al, Ti, Si)N layer, and constitutesan alternately laminated layer structure along with the thin layer A.

The thin layer B is provided as a layer for making up for theperformance (high-temperature toughness and high-temperature strength)which the thin layer A lacks.

As already described the thin layer A containing the Al and Sicomponents, in particular, has excellent wear resistance which thesecomponents provide. Also, the Cr component contained in the thin layer Acontributes for maintaining a predetermined chipping resistance andfracture resistance.

However, in order to use the coated tool under severe cuttingconditions, such as high-speed gear cutting, high-speed milling, andhigh-speed drilling, in which high temperature is generated, and a largeimpact and mechanical load is applied to its cutting edge; the thinlayer A is required to have far superior high-temperature toughness andhigh-temperature strength.

In order to secure these performances, the thin layer A including a morelarge amount of Cr is required.

However, in such thin layer A, the content ratios of Al and Si becomesmall.

In that case, the high-temperature hardness and high-temperatureoxidation resistance of the thin layer A become insufficient, and thewear resistance also becomes deteriorated. Therefore, it is impossibleto increase further the Cr content ratio in the thin layer A.

Thus, in this invention, the thin layer B composed of the (Al, Ti, Si)Nlayer is laminated alternately with the above thin layer A. By formingthe hard coating layer having an alternately laminated layer structureof the thin layers A and B on the tool; the thin layers A and B becomeadjacent to each other; and thus good performance of the thin layer B,namely the excellent high-temperature toughness and the high-temperaturestrength, can make up for such characters which the thin layer A lacks,without losing good characters of the thin layer A, namely, theexcellent high-temperature toughness and the thermoplastic deformationresistance. Therefore, the hard coating layer as a whole can exhibit theperformance; excellent chipping resistance, fracture resistance, andwear resistance.

The operational effects of the Al component and Si component in thecompositional formula of the thin layer B are the same as those of thethin layer A. However, if the U value (atomic ratio) indicating thecontent ratio of Al is less than 0.05, or the W value (atomic ratio)indicating the ratio of Si is less than 0.01; the required minimumpredetermined high-temperature hardness, high-temperature oxidationresistance, and thermoplastic deformation resistance cannot be achieved;and also such U value causes occurrence of wear resistancedeterioration.

Additionally, if the U value exceeds 0.75; the content ratio of Tidecreases relatively, and then the effects of improving thehigh-temperature toughness and high-temperature strength cannot beexpected from such U value.

If the W value exceeds 0.1, the wear-resistance improving effect shows atendency to decrease.

Therefore, the U value indicating the content ratio of Al was determinedin the range of 0.05 to 0.75; and also the W value indicating thecontent ratio of Si was determined in the range of 0.01 to 0.1.

Additionally, if the V value (atomic ratio) indicating the content ratioof Ti is less than 0.15; the effect of further improving the superiorityof the high-temperature toughness and high-temperature strength cannotbe expected. On the other hand, if the V value exceeds 0.94; requiredminimum high-temperature hardness and high-temperature oxidationresistance cannot be achieved due to a relative decrease in the contentratios of Al component and Si component.

Therefore, the V value indicating the content ratio of Ti was determinedin the range of 0.15 to 0.94.

In addition, especially preferable ranges regarding the above U, V, andW are 0.45≦U≦0.55, 0.4≦V≦0.5, and 0.03≦W≦0.07 respectively.

(c) Thickness of Layer

If the thicknesses of the thin layer A and the thin layer B are lessthan 0.01 μm; to form surly the thin layers having such thicknesses anda target composition is very difficult, and also the effect of improvingthe wear resistance by the thin layer A and the effect of improving thehigh-temperature toughness by the thin layer B cannot be achieved well.On the other hand, if the thicknesses of the thin layer A and the thinlayer B exceed 0.1 μm; the drawbacks of each thin layer, i.e., the lackof toughness and strength in the thin layer A, and the lack of wearresistance in the thin layer B, appear locally within the layers; andthen the risk, that the performance of the hard coating layer as a wholebecome deteriorated, will increase.

Therefore, the thicknesses of the thin layer A and the thin layer B weredetermined in the range of 0.01 to 0.1 μm, respectively.

The thin layer B is provided to compensate for the performance which islacking for the thin layer A.

Further, if the thicknesses of each thin layer A and B are within arange of 0.01 to 0.1 μm; the hard coating layer composed of thealternately laminated layer structure of each thin layer A and B, canperform as if to become one layer having the excellent high-temperaturetoughness and high-temperature strength without losing the excellenthigh-temperature hardness, high-temperature oxidation resistance, andthermoplastic deformation resistance.

However, if the thicknesses of the thin layer A and the thin layer Bexceed 0.1 μm; the lack of toughness and strength of the thin layer Aand the lack of wear resistance of the thin layer B shown.

Additionally, if the total thickness of the layer (upper layer) composedof an alternately laminated layer structure of the thin layer A and thethin layer B, is less than 1 μm; such layer cannot exhibit the aboveexcellent performance. On the other hand, if the total thickness exceeds10 μm; in such layer, chipping or fractures tends to arise. Thus, thetotal thickness of the layer (upper layer) composed of an alternatelylaminated layer structure of the thin layers A and B, was determined inthe range of 1 to 10 μm, preferably, 1 to 5 μm.

(d) Under Layer

If the alternately laminated layer structure mentioned above is composedby forming alternately the thin layers A and B directly on the surfaceof a tool substrate by using, for example, physical vapor deposition; acompressive residual stress will occur within the layers.

Further, if a coated tool provided with such hard coating layer is usedunder excessively severe cutting conditions, this compressive residualstress makes the adhesion strength between the tool substrate and thehard coating layer unstable.

Thus, in such a case, it is necessary to further enhance the adhesionstrength between the surface of the tool substrate and the hard coatinglayer having an alternately laminated layer structure.

As a means for enhancing the adhesion strength, to form a under layer,namely, a foundation layer, on the surface of the tool substrate iseffective.

In particular, in the present invention, the hard coating layer isconstructed of an upper layer and a under layer. The upper layer iscomposed of the alternately laminated layer structure of the thin layersA and B. The under layer is formed interposingly between the upper layerand the surface of the tool substrate.

Further, the formed under layer, in which

-   -   its thickness is from 0.5 to 10 μm, and    -   its composition is the same composition as the thin layer A or        the thin layer B, has an improved adhesion strength between the        tool substrate and the hard coating layer. Also, it is confirmed        that a coated tool with this under layer can perform stable        cutting processes without occurrences of peeling and/or fracture        in the hard coating layer, even if this tool is used under        excessively severe cutting conditions.

In addition, if the thickness of the under layer is less than 0.5 μm;such thickness does not give the effect of improving the adhesionstrength.

On the other hand, if the thickness exceeds 10 μm; the accumulation ofthe residual compressive stresses makes a crack easy to occur to thelayer, and then stable adhesion strength cannot be secured.

Thus, the thickness of the under layer was determined in the range of0.5 to 10 μm, preferably, 2 to 6 μm.

(e) Tool Substrate

Conventionally known various substrates, namely, bodies, such asWC-based cemented carbide, TiCN-based cermet, and high-speed tool steel(high-speed steel) are usable as the tool substrate of the coated tool.

On the surfaces of these various tool substrates, a hard coating layeris formed by using, for example, physical vapor deposition. In thiscase, in order to further enhance the adhesion strength between thesubstrate and the hard coating layers; the tool substrate, in which itssurface roughness is equal to or less than JIS (Japanese IndustrialStandards) Rz 1.6 μm, is preferable.

In addition, in this invention, a coated tool; in which its exteriorsurface is a colored layer, for example, a TiN layer (golden color) forthe purpose of the distinguishing between used and unused tools; isavailable. The thickness of 0.5 μm or less is sufficient for this layer.

Advantage of the Invention

In the surface-coated cutting tool of the present invention, the hardcoating layer is constructed of the alternately laminated layerstructure of the thin layer A, which is at least composed of an (Al, Cr,Si)N layer, and the thin layer B, which is composed of an (Al, Ti, Si)Nlayer. Such structure can provide excellent high-temperature hardness,high-temperature toughness, high-temperature strength, and thermoplasticdeformation resistance for the tool. Additionally, the tinder layer;which is formed as a lower layer, and has the same composition as thatof the thin layer A or the thin layer B; can improve the adhesionstrength.

Therefore, even if the tool is used in the high-speed gear cutting,high-speed milling, and high-speed drilling in which high temperature isgenerated, and a large impact and mechanical load is applied to acutting edge,

the hard coating layer can exhibit excellent high-temperature hardness,high-temperature toughness, high-temperature strength, and thermoplasticdeformation resistance. As a result, excellent fracture resistance andwear resistance can be exhibited for a prolonged period of time withoutthe occurrence of chipping, fractures, partial wear, and/or peeling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B shows an arc ion plating apparatus used for forming ahard coating layer of a coated tool of the invention, FIG. 1A is aschematic plan view and FIG. 1B is a schematic front view.

FIG. 2 is a schematic explanatory view of a conventional arc ion platingapparatus.

FIG. 3 is a schematic perspective view of a solid hob cutter.

FIG. 4 is a schematic perspective view of a disc type shaper cutter.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, a coated tool of the invention will be specifically described bymeans of examples.

EXAMPLE 1

High-speed steel gear cutter bodies, namely, substrates, (solid hobcutters) having a shape shown in FIG. 3 were prepared. The material ofthese solid hob cutters is high-speed tool steels of JIS-SKH51 orJIS-SKH55, and has a cylindrical shape in which dimensions are, Diameter90 mm×Length 130 mm. Further, by machining the material, the high-speedsteel gear cutter bodies (solid hob cutters) were manufactured. Thesesolid hob cutters have a shape in which overall dimensions are Diameter85 mm×Length 100 mm. Also these solid hob cutters are counterclockwisequadruple thread gears hob cutter having 16 gashes.

The following procedure of (a) to (d) was carried on to manufacturecoated high-speed steel gear cutters (solid hob cutter).

(a) Each high-speed steel gear cutter body (solid hob cutter) made ofthe above two kinds of material is cleaned by ultrasonic cleaning inacetone, and then dried. Thereafter, each body is placed on a turntableof an arc ion plating apparatus shown in FIG. 1. The position, whereeach body is placed, is radially outwardly apart from the central axisof the turntable with a predetermined distance, and is by the side ofthe turntable's outer peripheral portion.

A cathode (evaporation source) located at a one side, left side in FIG.1, is an Al—Cr—Si alloy for formation of a thin layer A, and has acomponent composition corresponding to a target composition shown inTable 1. Another cathode (evaporation source) located at the other side,right side in FIG. 1, is an Al—Ti—Si alloy for formation of a thin layerB, and has a component composition corresponding to a target compositionshown in Table 1. These cathodes are arranged to face each other acrossthe turntable. (In the case that the two types of cathodes are there,one of cathodes for formation of the thin layers A and B can be usedalso as a cathode for formation of a under layer. In addition, a thirdelectrode as the electrode only for formation of a under layer is quitepossible to be provided.)

(b) The inside of the apparatus is evacuated to a pressure of 0.1 Pa orless; and then keeping this pressure level, the inside of the apparatusis heated up to 400° C. with a heater. Further, turning the turntable, aDC bias voltage of −800 V is applied to a gear cutter body, which isrotating and is placed on the turntable. Additionally, applying acurrent of 100 A between an anode and an electrode for bombardmentcleaning (for example, an Al—Cr—Si alloy for formation of the thin layerA,) to generate arc discharge; and then the surface of the gear cutterbody becomes clear by bombardment cleaning treatment.(c) A nitrogen gas as a reaction gas is introduced into the apparatus tocreate a reaction atmosphere of 3 Pa; and also a DC bias voltage of −35to −45 V is applied to the gear cutter body, which is rotating and isplaced on the turntable which is turning.

Additionally, applying a current of 100 A between an anode and anAl—Cr—Si alloy for formation of the thin layer A, an arc discharge isgenerated.

Thereby, a under layer having a target composition and a targetthickness as shown in Table 1 is vapory deposited and formed on thesurface of the high-speed steel gear cutter body. (For example, an underlayer having same composition of the thin layer A or B is usable.) Incase that the under layer is not to be formed, naturally the aboveprocess (c) is unnecessary.

(d) Next, a nitrogen gas as a reaction gas is introduced into theapparatus to create a reaction atmosphere of 2 Pa; and also a DC biasvoltage of −25 to −35 V is applied to the gear cutter body, which isrelating and is placed on the turntable which is turning. Additionally,applying a predetermined current in the range of 50 to 200 A between theanode and the cathode made of an Al—Ti—Si alloy for formation of thethin layer B, an arc discharge is generated between them.

Thereby, the thin layer B having a predetermined thickness is formed onthe under layer covering the surface of the high-speed steel gear cutterbody.

After forming such shin layer B, the arc discharge is stopped.

Subsequently, applying a predetermined current in the range of 50 to 200A between the anode and a cathode made of an Al—Cr—Si alloy forformation of the thin layer A, an arc discharge is generated betweenthem.

Thereby, the thin layer A having a predetermined thickness is formed onthe thin layer B. After forming such shin layer A, the arc discharge isstopped.

(If the under layer has the same composition as the thin layer B, theformation of the thin layer A may be started firstly.)

Thereafter, the above processes for forming alternately the thin layersB and A are performed repeatedly, wherein:

the process for the formation of the thin layer B is by the arcdischarge between the anode and the cathode made of an Al—Ti—Si alloyfor formation of the thin layer B, and the process for the formation ofthe thin layer A is by the arc discharge between the anode and thecathode made of an Al—Cr—Si alloy for formation of the thin layer A. Inaccordance with the procedure of (a) to (d) aforementioned, coatedhigh-speed steel gear cutters (solid hob cutter) 1 to 8 of the inventionwere manufactured. On the surfaces of these tools, a under layer and anupper layer are deposited. The under layer has a target composition anda target thickness shown in Table 1. The upper layer is composed ofalternately laminated layers of the thin layers A and B having targetcompositions and target thicknesses across their thicknesses,respectively shown in Table 1.

In addition, the under layer is not provided in the coated high-speedsteel gear cutters 1 and 5 of the invention.

Additionally, for the purpose of comparison, coated high-speed steelgear cutters (solid hob cutter) with a single phase structure coatinglayer, namely, a single layer structure coating layer, was manufacturedthrough the following procedure.

Each high-speed steel gear cutter body made of the aforementioned twokinds of material is cleaned by ultrasonic cleaning in acetone, and thendried. Thereafter, each body is placed into an arc ion plating apparatusshown in FIG. 2. An Al—Cr—Si alloy having a component compositioncorresponding to a target composition shown in Table 2 is also placedinto the arc ion plating apparatus as a cathode (evaporation source).First, the inside of the apparatus is evacuated to a pressure of 0.1 Paor less; and then keeping this pressure level, the inside of theapparatus is heated up to 400° C. with a heater.

Applying a DC bias voltage of −800 V to a gear cutter body, and alsoapplying a current of 100 A between an anode and a cathode made of theabove Al—Cr—Si alloy (or the Al—Ti—Si alloy), an arc discharge isgenerated; and then the surface of the gear cutter body becomes clear bybombardment cleaning treatment with the Al—Cr—Si alloy (or the Al—Ti—Sialloy).

Next, a nitrogen gas as a reaction gas is introduced into the apparatusto create a reaction atmosphere of 3 Pa, and the DC bias voltage appliedto the gear cutter body is decreased in the range of −35 to −45 V; andthen an arc discharge is generated between the anode and the Al—Cr—Sialloy (or the Al—Ti—Si alloy).

Thereby, coated high-speed steel gear cutters 1 to 8 with a single layerstructure coating layer (hereinafter, referred to as comparative coatedhigh-speed steel gear cutters 1 to 8) were manufactured. On the surfaceof these tools, a hard coating layer composed of an (Al, Cr, Si)N layer(or a hard coating layer composed of an (Al, Ti, Si)N layer) isdeposited. This hard coating layer has a single layer structure with atarget composition and a target thickness shown in Table 2.

Next, the performances in cutting of the above coated high-speed steelgear cutters 1 to 8 of the invention and of the above comparative coatedhigh-speed steel gear cutters 1 to 8 were measured.

Using these tools, a workpiece made of JIS-SCr420H was machined toproduct a gear with the following dimensions and shapes,

Module: 1.75,

Pressure angle: 17.5°,

Number of teeth: 48,

Helical angle: 25° left twist, and

Face width is 50 mm;

under the following conditions,

Cutting speed (rotating speed): 250 m/min,

Feed: 2.5 mm/rev, and

cutting type: climbing, no shifting, and air blowing.

This test was performed as a high-speed gear cutting. (In addition, thecutting speed in this test of a gear made from this workpiece istypically 200 m/min.) Until the wear width of the flank face became 0.2mm, this cutting test was performed repeatedly; and then the number ofgears machined by the sample tool was counted.

The measurement results are shown in Tables 1 and 2.

EXAMPLE 2

Additionally, other high-speed steel gear cutter bodies having a relatedshape to a disc type shaper cutter body (100 Type described inJIS-B-4356) shown in a schematic perspective view in FIG. 4 wereprepared. These bodies have a shape in which overall dimensions arePitch circle diameter 100 mm×Thickness 18 mm and its number of cutterteeth is 50.

The material of these bodies is high-speed tool steels of JIS-SKH51 orJIS-SKH55, and has a cylindrical shape in which dimensions are Diameter100 mm×Thickness 130 mm. By machining the material, the high-speed steelgear cutter bodies (100 Type described in JIS-B-4356) were manufactured.

The following procedure was carried on to manufacture coated high-speedsteel gear cutters (shaper cutter).

The surface of each high-speed steel gear cutter body (shaper cutter) iscleaned by ultrasonic cleaning in acetone, and then dried. Thereafter,each body is placed into the arc ion plating apparatus shown in FIG. 1.Further, under the same conditions as Example 1 aforementioned, thecoated high-speed steel gear cutters (shaper cutter) 9 to 16 of theinvention were manufactured. On the surfaces of these tools, an underlayer and an upper layer are deposited. The under layer has a targetcomposition and a target thickness shown in Table 1. The upper layer iscomposed of alternately laminated layers of the thin layers A and Bhaving target compositions and target thicknesses across theirthicknesses, respectively shown in Table 1. In addition, the under layeris not provided in the coated high-speed steel gear cutters 9 and 13 ofthe invention.

Additionally, for the purpose of comparison, coated high-speed steelgear cutters (shaper cutter) with a single layer structure coating layerwere manufactured through the following procedure.

Each surface of these high-speed steel gear cutter bodies is cleaned byultrasonic cleaning in acetone, and then dried. Thereafter, each body isplaced into an arc ion plating apparatus shown in FIG. 2. Further, underthe same conditions as Example 1 aforementioned, coated high-speed steelgear cutters 9 to 16 with a single layer structure coating layer(hereinafter, referred to as comparative coated high-speed steel gearcutters 9 to 16) were manufactured.

On the surface of these tools, a hard coating layer composed of an (Al,Cr, Si)N layer (or a hard coating layer composed of an (Al, Ti, Si)Nlayer) is deposited. This hard coating layer has a single layerstructure with a target composition and a target thickness shown inTable 2.

Next, the performances in cutting of the above coated high-speed steelgear cutters 9 to 16, and of the above comparative coated high-speedsteel gear cutters 9 to 16; were measured.

Using these tools, a workpiece made of JIS-SCr420H was machined toproduct a gear with the following dimensions and/or shapes,

Module: 2,

Pressure angle: 20°,

Number of teeth: 15, and

Face width: 22.5 mm;

under the following conditions,

Number of strokes: 1200 stroke/min,

Circumferential feed: 0.3 mm/stroke, and

Radial feed: 0.03 mm/stroke.

This test was performed as high-speed gear cutting. (In addition, thecutting speed in this test of a gear made from this workpiece istypically 800 stroke/min.)

Until the wear width of the sample tool's flank face became 0.2 mm, thiscutting test was performed repeatedly; and then the number of gearsmachined by the sample tool was counted.

The measurement results are shown in Tables 1 and 2.

Each content ratio regarding an Al component, a Cr component, a Ticomponent, and a Si component as a target composition in Tables 1, 2,and 4 to 9; is shown in terms of atomic ratio.

TABLE 1 HARD COATING LAYER UPPER LAYER/THIN LAYER-A MATERIAL UNDER LAYERONE-LAYER OF TARGET TARGET TARGET TARGET BODY COMPOSITION LAYERCOMPOSITION LAYER (SUB- (ATOMIC RATIO) THICKNESS (ATOMIC RATIO)THICKNESS TYPE STRATE) Al Cr Ti Si (μm) Al Cr Si (nm) COATED 1 SKH51 — —— — — 0.24 0.75 0.01 10 HIGH- 2 SKH51 0.24 0.75 — 0.01 1 0.24 0.75 0.0110 SPEED 3 SKH51 0.47 — 0.50 0.03 2 0.45 0.52 0.03 30 STEEL 4 SKH51 0.420.52 — 0.06 3.5 0.42 0.52 0.06 50 GEAR 5 SKH55 — — — — — 0.43 0.49 0.0850 CUTTING 6 SKH55 0.53 — 0.40 0.07 5 0.43 0.49 0.08 50 TOOL OF 7 SKH550.20 0.60 — 0.20 7 0.20 0.60 0.20 70 THE 8 SKH55 0.15 — 0.80 0.05 100.30 0.65 0.05 100 INVEN- 9 SKH51 — — — — — 0.35 0.55 0.10 70 TION 10SKH51 0.35 0.55 — 0.10 4 0.35 0.55 0.10 70 11 SKH51 0.55 — 0.40 0.05 20.45 0.45 0.10 40 12 SKH51 0.45 0.40 — 0.15 1 0.45 0.40 0.15 60 13 SKH55— — — — — 0.20 0.75 0.05 80 14 SKH55 0.05 — 0.94 0.01 10 0.20 0.75 0.0580 15 SKH55 0.30 0.55 — 0.15 7 0.30 0.55 0.15 100 16 SKH55 0.35 — 0.630.02 5 0.40 0.45 0.15 20 HARD COATING LAYER UPPER LAYER/THIN LAYER BONE-LAYER UPPER LAYER TARGET TARGET TOTAL NUMBER COMPOSITION LAYERTARGET LAYER OF (ATOMIC RATIO) THICKNESS THICKNESS MACHINED TYPE Al TiSi (NM) (μm) GEAR COATED 1 0.75 0.24 0.01 20 1 90 HIGH- 2 0.75 0.24 0.0120 1 100 SPEED 3 0.47 0.50 0.03 50 5 110 STEEL 4 0.50 0.45 0.05 70 1.5115 GEAR 5 0.53 0.40 0.07 30 3 95 CUTTING 6 0.53 0.40 0.07 30 3 110 TOOLOF 7 0.05 0.85 0.10 40 10 100 THE 8 0.15 0.80 0.05 80 5 105 INVEN- 90.45 0.48 0.07 50 2 95 TION 10 0.45 0.48 0.07 50 2 110 11 0.55 0.40 0.0510 6 110 12 0.75 0.15 0.10 100 7 100 13 0.05 0.94 0.01 90 3 90 14 0.050.94 0.01 90 3 100 15 0.70 0.25 0.05 60 1 105 16 0.35 0.63 0.02 10 4 105

TABLE 2 HARD COATING LAYER MATERIAL TARGET NUMBER OF TARGET COMPOSITIONLAYER OF BODY (ATOMIC RATIO) THICKNESS MACHINED TYPE (SUBSTRATE) Al CrTi Si (μm) GEAR COMPARATIVE 1 SKH51 0.75 — 0.24 0.01 1 20 HIGH-SPEED 2SKH51 0.24 0.75 — 0.01 2 25 STEEL 3 SKH51 0.47 — 0.50 0.03 7 35 GEAR 4SKH51 0.42 0.52 — 0.06 5 40 CUTTING 5 SKH55 0.43 0.49 — 0.08 3 22 TOOL 6SKH55 0.53 — 0.40 0.07 8 30 7 SKH55 0.20 0.60 — 0.20 17 25 8 SKH55 0.15— 0.80 0.05 15 30 9 SKH51 0.45 — 0.48 0.07 2 22 10 SKH51 0.35 0.55 —0.10 6 40 11 SKH51 0.55 — 0.40 0.05 8 35 12 SKH51 0.45 0.40 — 0.15 8 3513 SKH55 0.20 0.75 — 0.05 3 20 14 SKH55 0.05 — 0.94 0.01 13 25 15 SKH550.30 0.55 — 0.15 8 33 16 SKH55 0.35 — 0.63 0.02 9 28

The compositions of the layers, namely, the under layer, the thin layerA, and the thin layer B, which constitute the hard coating layer of thecoated high-speed steel gear cutters 1 to 16 of the invention and thecompositions of the hard coating layers of the comparative coatedhigh-speed steel gear cutters 1 to 16 were measured by an energydispersive X-ray analysis method using a transmission electronmicroscope. The results of this measurement show that each layer has asubstantially same composition as its target composition respectively.

Additionally, the thickness of each layer constituting the above hardcoating layer was section-measured by the transmission electronmicroscope. The results of this measurement show that each layer has anaverage thickness (average of five points) which is substantially samethickness as its target thickness.

The results in Tables 1 and 2 show clearly the following subjects.

The hard coating layer of each of the coated high-speed steel gearcutters of the invention

-   -   is constituted by the alternately laminated layer of the thin        layer A and the thin layer B, and/or the under layer;    -   has excellent high-temperature hardness and thermoplastic        deformation resistance, and    -   has also excellent high-temperature toughness and        high-temperature strength.

Therefore, even in the cutting performed under the high-speed gearcutting conditions in which high temperature is generated, and a largeimpact and/or mechanical load is applied; the hard coating layer canexhibit its excellent wear resistance without the occurrence of chippingor fractures.

On the other hand, if a comparative coated high-speed steel gear cutter,on which a hard coating layer composed of an (Al, Cr, Si)N layer (or ahard coating layer composed of an (Al, Ti, Si)N layer) having a singlelayer structure is formed, is used under the above high-speed gearcutting conditions; such tool's insufficient toughness will causefractures or chipping. Also, such tool's poor wear resistance makes itstool life relatively short period.

EXAMPLE 3

As the first step, the following procedure was carried on to manufacturecemented carbide end mills.

Material powders,

-   -   a medium coarse-grained WC powder having an average grain size        of 5.5 μm,    -   a fine-grained WC powder having an average grain size of 0.8 μm,    -   a TaC powder having an average grain size of 1.3 μm,    -   an NbC powder having an average grain size of 1.2 μm,    -   a ZrC powder having an average grain size of 1.2 μm,    -   a Cr₃C₂ powder having an average grain size of 2.3 μm,    -   a VC powder having an average grain size of 1.5 μm,    -   a (Ti, W)C [TiC/WC=50/50 in a mass ratio] having an average        grain size of 1.0 μm, and    -   a Co powder having an average grain size of 1.8 μm;        are prepared as raw powders for the cemented carbide end mills.

These raw powders are blended in accordance with a blending compositionshown in Table 3. After adding wax to the blended raw powders, theblended raw powders are well mixed in acetone for 24 hours by a ballmill, and then dried in a decompression atmosphere.

Thereafter, the mixed powders are pressed with a pressure of 100 MPa toform various green compacts having a predetermined shape.

In a vacuum atmosphere of 6 Pa, these green compacts are heated upgradually at a temperature rising rate of 7° C./min to a predeterminedtemperature in the range of 1370 to 1470° C. After keeping thistemperature for one hour, these green compacts are sintered under thecondition of furnace cooling.

Therefore, three types of sintered compact for the formation of cementedcarbide substrates are formed. These sintered compacts have round barshapes with diameters 8 mm, 13 mm, and 26 mm, respectively. Further, bygrinding these three types of round bar sintered compacts, cementedcarbide end mills 1 to 11 made of a WC-based cemented carbide alloy weremanufactured.

These end mills 1 to 11 have a four-flute square shape with a helixangle of 30°, and their dimensions in which a diameter×length are 6mm×13 mm, 10 mm×22 mm, or 20 mm×45 mm respectively. Table 3 also showsthe combinations of the diameter×length and the blending composition.

Next, the following procedure was carried on, to form a coating layer onthe above cemented carbide end mills.

The surfaces of these cemented carbide end mills 1 to 11 are cleaned byultrasonic cleaning in acetone, and then dried. Thereafter, these endmills are placed into the arc ion plating apparatus shown in FIG. 1.Under the same conditions as Example 1 aforementioned, surface-coatedcemented carbide end mills 1 to 11 (hereinafter referred to as coatedcemented carbide end mills 1 to 11 of the invention) were manufactured,as the surface-coated cutting tools of the invention. On the surfaces ofthese end mills, a under layer and an upper layer are deposited. Theunder layer has a target composition and a target thickness shown inTable 4. The upper layer is composed of alternately laminated layers ofthe thin layers A and B having target compositions and targetthicknesses across their thicknesses, respectively shown in Table 4.

In addition, the under layer is not provided in the surface-coatedcemented carbide end mills 1, 5, and 9 of the invention.

Additionally, for the purpose of comparison, comparative surface-coatedcemented carbide end mills with a single layer structure coating layer(hereinafter referred to as comparative coated cemented carbide endmills) were manufactured through the following procedure.

The surfaces of the above cemented carbide end mills 1 to 11 are cleanedby ultrasonic cleaning in acetone, and then dried. Thereafter, the endmills are placed into an arc ion plating apparatus shown in FIG. 2.Under the same conditions as Example 1 aforementioned, the comparativecoated cemented carbide end mills 1 to 11 having a hard coating layerwere manufactured. The hard coating layer has a single layer structurewith a target composition and a target thickness respectively shown inTable 5.

(a) Next, the performances in cutting of the above coated cementedcarbide end mills 1 to 11 of the invention, and of the above comparativecoated cemented carbide end mills 1 to 11 were evaluated with acondition mentioned in the below (a1), (a2) or (a3).

(a1) For the coated cemented carbide end mills 1 to 4 of the inventionand the comparative coated cemented carbide end mills 1 to 4, a cuttingtest, in which these end mills try to machine a die steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 150 m/min,

Depth of slot (depth of cut): 1.0 mm, and

Table feed: 1000 mm/min.

Additionally, the workpiece is a plate of JIS-SKD61 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling of diesteel. (Typical cutting speed of this cutting is 120 m/min.)

(a2) For the coated cemented carbide end mills 5 to 8 of the inventionand the comparative coated cemented carbide end mills 5 to 8, a cuttingtest, in which these end mills try to machine an alloy steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 160 m/min,

Depth of slot (depth of cut): 1.0 mm, and

Table feed: 1200 mm/min.

Additionally, the workpiece is a plate of JIS-SCM440 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling ofalloy steel. (Typical cutting speed of tins cutting is 100 m/min.)

(a3) For the coated cemented carbide end mills 9 to 11 of the inventionand the comparative coated cemented carbide end mills 9 to 11, a cuttingtest, in which these end mills try to machine a cold-die steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 100 m/min,

Depth of slot (depth of cut): 1.0 mm, and

Table feed: 600 mm/min,

Additionally, the workpiece is a plate of JIS-SKD11 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling ofcold-die steel.

(Typical cutting speed of this cutting is 50 m/min.)

Each slot milling test mentioned in the above (a1), (a2) or (a3) wasperformed repeatedly until the wear width of a flank face of the sampleend mill became 0.1 mm. Then the length of slot, which the sample endmill has cut, was measured. The flank face is located at a peripheralcutting edge of a cutting edge portion. This 0.1 mm is a standard of endmil's life for judging whether an end mill is usable or not. The testresults are shown in Tables 4 and 5.

TABLE 3 SYMBOL DIAMETER × OF LENGTH OF BODY CUTTING EDGE (SUB- BLENDINGCOMPOSITION (MASS %) PORTION TYPE STRATE) Co (Ti, W)C TaC NbC ZrC Cr₃C₂VC WC (mm) RAW (A) 5  5 — — — — — MEDIUM COARSE  6 × 13 POWDER GRAIN:REMAINDER FOR (B) 6 —  1 0.5 — — — FINE GRAIN:  6 × 13 CEMENTEDREMAINDER CARBIDE (C) 6 —  1 —  1 0.5 0.5 FINE GRAIN:  6 × 13 END MILLREMAINDER (D) 8 — — — — 0.5 0.5 FINE GRAIN: 10 × 22 REMAINDER (E) 9 2510 1 — — — MEDIUM COARSE 10 × 22 GRAIN: REMAINDER (F) 10 — — — — 1 —FINE GRAIN: 10 × 22 REMAINDER (G) 12 17  9 1 — — — MEDIUM COARSE 20 × 45GRAIN: REMAINDER (H) 16 — 10 5 10 — 13 MEDIUM COARSE 20 × 45 GRAIN:REMAINDER

TABLE 4 HARD COATING LAYER UPPER LAYER/THIN LAYER A SYMBOL UNDER LAYERTARGET ONE-LAYER OF TARGET TARGET COMPOSITION TARGET BODY COMPOSITIONLAYER (ATOMIC LAYER (SUB- (ATOMIC RATIO) THICKNESS RATIO) THICKNESS TYPESTRATE) Al Cr Ti Si (μm) Al Cr Si (nm) COATED  1 (A) — — — — — 0.35 0.550.10 10 CEMENTED  2 (A) 0.35 0.55 — 0.10 1 0.35 0.55 0.10 10 CARBIDE  3(B) 0.45 — 0.48 0.07 2 0.45 0.52 0.03 30 END MILL  4 (C) 0.05 — 0.940.01 6 0.20 0.75 0.05 90 OF THE  5 (D) — — — — — 0.42 0.52 0.06 50INVENTION  6 (D) 0.42 0.52 — 0.06 3.5 0.42 0.52 0.06 50  7 (E) 0.15 —0.80 0.05 5 0.30 0.65 0.05 50  8 (F) 0.40 0.45 — 0.15 7 0.40 0.45 0.1570  9 (G) — — — — — 0.45 0.45 0.10 40 10 (G) 0.45 0.45 — 0.10 4 0.450.45 0.10 40 11 (H) 0.75 — 0.15 0.10 10 0.45 0.40 0.15 100 HARD COATINGLAYER UPPER LAYER/ UPPER THIN LAYER B LAYER TARGET ONE-LAYER TOTALCOMPOSITION TARGET TARGET (ATOMIC LAYER LAYER LENGTH OF RATIO) THICKNESSTHICKNESS SLOT TYPE Al Ti Si (nm) (μm) (m) COATED  1 0.47 0.50 0.03 20 185 CEMENTED  2 0.47 0.50 0.03 20 1 98 CARBIDE  3 0.45 0.48 0.07 50 5 100END MILL  4 0.05 0.94 0.01 60 8 93 OF THE  5 0.50 0.45 0.05 70 1.5 90INVENTION  6 0.50 0.45 0.05 70 1.5 105  7 0.15 0.80 0.05 30 3 95  8 0.350.63 0.02 40 10 94  9 0.55 0.40 0.05 30 4 88 10 0.55 0.40 0.05 30 4 10311 0.75 0.15 0.10 80 5 92

TABLE 5 SYMBOL HARD COATING LAYER OF TARGET LENGTH BODY TARGETCOMPOSITION LAYER OF (SUB- (ATOMIC RATIO) THICKNESS SLOT TYPE STRATE) AlCr Ti Si (μm) (m) COMPARATIVE 1 (A) 0.47 — 0.50 0.03 1 28 COATED 2 (A)0.35 0.55 — 0.10 2 35 CEMENTED 3 (B) 0.45 — 0.48 0.07 7 40 CARBIDE 4 (C)0.05 — 0.94 0.01 14 32 END MILL 5 (D) 0.50 — 0.45 0.05 1.5 31 6 (D) 0.420.52 — 0.06 5 38 7 (E) 0.15 — 0.80 0.05 8 33 8 (F) 0.40 0.45 — 0.15 1732 9 (G) 0.55 — 0.40 0.05 4 30 10 (G) 0.45 0.45 — 0.10 8 36 11 (H) 0.75— 0.15 0.10 15 34

EXAMPLE 4

Round bar materials made of high-speed tool steel (JIS-SKH55) with threedifferent dimensions, namely, the diameter is 8 mm, 13 mm, or 26 mm,were prepared. By machining these three types of round bar materials,high-speed steel end mills 1 to 9 were manufactured. These end mills 1to 9 have a four-flute square shape with a helix angle of 30°, andcutting edges of them have a dimension in which its diameter×length is 6mm×13 mm, 10 mm×22 mm, or 20 mm×45 mm.

In addition, the dimensions and shapes of these high-speed steel endmills 1 to 3, 4 to 6, and 7 to 9 are the same as those of the cementedcarbide end mills 1 to 4, 5 to 8, 9 to 11 described in Example 3,respectively.

Next, the following procedure was carried on, to form a coating layer onthe above high-speed steel end mills.

The surfaces of these high-speed steel end mills 1 to 9 are cleaned byultrasonic cleaning in acetone, and then dried. Thereafter, these endmills are placed into the arc ion plating apparatus shown in FIG. 1.Under the same conditions as Example 1 aforementioned, surface-coatedhigh-speed steel end mills (hereinafter referred to as coated high-speedsteel end mills of the invention) 1 to 9 were manufactured, as thesurface-coated cutting tools of the invention. On the surfaces of theseend mills, a under layer and an upper layer are deposited. The underlayer has a target composition and a target thickness shown in Table 6.The upper layer is composed of alternately laminated layers of the thinlayers A and B having target compositions and target thicknesses acrosstheir thicknesses, respectively shown in Table 6.

In addition, the under layer is not provided in the coated high-speedsteel end mills 1, 4, and 7 of the invention.

Additionally, for the purpose of comparison, comparative surface-coatedhigh-speed steel end mills with a single layer structure coating layer(hereinafter referred to as comparative coated high-speed steel endmills) were manufactured through the following procedure.

The surfaces of the above coated high-speed steel end mills 1 to 8 arecleaned by ultrasonic cleaning in acetone, and then dried. Thereafter,the end mills are placed into the arc ion plating apparatus shown inFIG. 2. Under the same conditions as Example 1 aforementioned, thecomparative coated high-speed steel end mills 1 to 9 having a hardcoating layer was manufactured. The hard coating layer has a singlelayer structure with a target composition and a target thicknessrespectively shown in Table 7.

(b) Next, the performances in cutting of the above coated high-speedsteel end mills 1 to 9 of the invention and the above comparative coatedhigh-speed steel end mills 1 to 9 were evaluated with a conditionmentioned in the below (b1), (b2) or (b3).

(b1) For the coated high-speed steel end mills 1 to 3 of the inventionand the comparative coated high-speed steel end mills 1 to 3, a cuttingtest, in which these end mills try to machine a carbon steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 60 m/min,

Depth of slot (depth of cut): 6 mm, and

Table feed: 400 mm/min.

Additionally, the workpiece is a plate of JIS-S55C with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling ofcarbon steel. (Typical cutting speed of this cutting is 30 m/min.)

(b2) For the coated high-speed steel end mills 4 to 6 of the inventionand the comparative coated high-speed steel end mills 4 to 6, a cuttingtest, in which these end mills try to machine a die steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 50 m/min,

Depth of slot (depth of cut): 10 mm, and

Table feed: 400 mm/min.

Additionally, the workpiece is a plate of JIS-SKD61 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling of diesteel. (Typical cutting speed of this cutting is 25 m/min.)

(b3) For the coated high-speed steel end mills 7 to 9 of the inventionand the comparative coated high-speed steel end mills 7 to 9, a cuttingtest, in which these end mills try to machine an alloy steel as aworkpiece, was carried out under the following conditions,

Cutting speed: 50 m/min,

Depth of slot (depth of cut): 20 mm, and

Table feed: 350 mm/min.

Additionally, the workpiece is a plate of JIS-SCM440 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a dry high-speed slot milling ofalloy steel. (Typical cutting speed of this cutting is 25 m/min.)

Each slot milling test mentioned in the above (b1), (b2) or (b3) wasperformed repeatedly until the wear width of a flank face of the sampleend mill became 0.1 mm. Then the length of slot, which the sample endmill has cut, was measured. The flank face is located at a peripheralcutting edge of a cutting edge portion. This 0.1 mm is a standard of endmill's life for judging whether an end mill is usable or not. The testresults are shown in Tables 6 and 7.

TABLE 6 HARD COATING LAYER UPPER LAYER/THIN LAYER A UNDER LAYERONE-LAYER TARGET TARGET TARGET TARGET SYMBOL COMPOSITION LAYERCOMPOSITION LAYER OF (ATOMIC RATIO) THICKNESS (ATOMIC RATIO) THICKNESSTYPE BODY Al Cr Ti Si (μm) Al Cr Si (nm) COATED 1 (A) — — — — — 0.350.55 0.10 70 HIGH SPEED 2 (B) 0.35 0.55 — 0.10  4 0.35 0.55 0.10 70STEEL 3 (C) 0.15 — 0.80 0.05 10 0.30 0.65 0.05 80 END MILL 4 (D) — — — —— 0.40 0.45 0.15 60 OF THE 5 (E) 0.40 0.45 — 0.15  1 0.40 0.45 0.15 60INVENTION 6 (F) 0.45 — 0.48 0.07  2 0.45 0.52 0.03 40 7 (G) — — — — —0.45 0.45 0.10 100 8 (G) 0.45 0.45 — 0.10  7 0.45 0.45 0.10 100 9 (H)0.05 — 0.94 0.01  5 0.20 0.75 0.05 20 HARD COATING LAYER UPPER UPPERLAYER/THIN LAYER B LAYER TARGET ONE-LAYER TOTAL COMPOSITION TARGETTARGET LENGTH (ATOMIC LAYER LAYER OF RATIO) THICKNESS THICKNESS SLOTTYPE Al Ti Si (nm) (μm) (m) COATED 1 0.47 0.50 0.03 50 2 20 HIGH SPEED 20.47 0.05 0.03 50 2 35 STEEL 3 0.15 0.80 0.05 90 3 25 END MILL 4 0.350.63 0.02 100 7 18 OF THE 5 0.35 0.63 0.02 100 7 28 INVENTION 6 0.450.48 0.07 10 6 30 7 0.55 0.40 0.05 60 1 20 8 0.55 0.40 0.05 60 1 26 90.05 0.94 0.01 10 4 23

TABLE 7 HARD COATING LAYER TARGET LENGTH SYMBOL TARGET COMPOSITION LAYEROF OF (ATOMIC RATIO) THICKNESS SLOT TYPE BODY Al Cr Ti Si (μm) (m)COMPARATIVE 1 (A) 0.47 — 0.50 0.03 2 6 COATED 2 (B) 0.35 0.55 — 0.10 610 HIGH-SPEED 3 (C) 0.15 — 0.80 0.05 13 8 STEEL 4 (D) 0.35 — 0.63 0.02 75.5 END MILL 5 (E) 0.40 0.45 — 0.15 8 8 6 (F) 0.45 — 0.48 0.07 8 9.5 7(G) 0.55 — 0.40 0.05 1 6 8 (G) 0.45 0.45 — 0.10 8 7.5 9 (H) 0.05 — 0.940.01 9 7

The compositions of the layers, namely, the under layer and the upperlayer composed of an alternately laminated layer structure of the thinlayers A and B, which constitute the hard coating layer of the coatedcemented carbide end mills 1 to 11 of the invention and the coatedhigh-speed steel end mills 1 to 9 of the invention in Examples 3 and 4;also the composition of the hard coating layer of the comparative coatedcemented carbide end mills 1 to 11 and the comparative coated high-speedsteel end mills 1 to 9; were measured by an energy dispersive X-rayanalysis method using a transmission electron microscope.

The results of this measurement show that each layer has a substantiallysame composition as its target composition respectively.

Additionally, the thickness of each layer constituting the above hardcoating layer was section-measured by the transmission electronmicroscope. The results of this measurement show that each layer has anaverage thickness (average of five points) which is substantially samethickness as its target thickness.

The results in Tables 4 to 7 show clearly the following facts.

The hard coating layer of the coated cemented carbide end mills of theinvention and the coated high-speed steel end mills of the invention

-   -   is constituted by the alternately laminated layer of the thin        layer A and the thin layer B, and/or the under layer;    -   has excellent high-temperature hardness and thermoplastic        deformation resistance, and    -   has also excellent high-temperature toughness and        high-temperature strength.

Therefore, even in the cutting performed under the high-speed millingconditions in which high temperature is generated, and a large impactand/or mechanical load is applied, the hard coating layer can exhibitits excellent wear resistance without the occurrence of chipping orfractures.

On the other hand, if a comparative coated cemented carbide end mill anda comparative coated high-speed end mill, on which a hard coating layercomposed of an (Al, Cr, Si)N layer (or a hard coating layer composed ofan (Al, Ti, Si)N layer) having a single layer structure is formed, isused under the above high-speed milling conditions; such end mill'sinsufficient toughness causes fractures or chipping. Also, such endmill's poor wear resistance makes its usable life time relatively shortperiod.

EXAMPLE 5

As the first step, three types of sintered compacts produced in theabove Example 3 having round bar shapes with diameters 6 mm body symbols(A) to (C) of raw powders for cemented carbide end mills), 10 mm bodysymbols (D) to (F) of raw powders for cemented carbide end mills), or 20mm body symbols (G) and (H) of raw powders for cemented carbide endmills) were prepared. By grinding these three types of round barsintered compacts, cemented carbide drills 1 to 11 made of a WC-basedcemented carbide alloy were manufactured.

These drills 1 to 11 have a two-flute shape with a helix angle of 30°,and web sections of them have a dimension in which a diameter×length is4 mm×13 mm for the drills 1 to 4, 10 mm×22 mm for the drills 5 to 8, or20 mm×45 mm for the drills 9 to 11.

Next, after a honing process was performed on the cutting edges of thesecemented carbide drills 1 to 11; they were also cleaned by ultrasoniccleaning in acetone, and then dried. Thereafter, these drills wereplaced into the arc ion plating apparatus shown in FIG. 1. Under thesame conditions as Example 1 aforementioned, surface-coated cementedcarbide drills 1 to 11 (hereinafter referred to as coated cementedcarbide drills 1 to 11 of the invention) were manufactured. On thesurfaces of these drills, a under layer and an upper layer aredeposited. The under layer has a target composition and a targetthickness shown in Table 8. The upper layer is composed of alternatelylaminated layers of the thin layers A and B having target compositionsand target thicknesses across their thicknesses, respectively shown inTable 8.

In addition, the under layer is not provided in the surface-coatedcemented carbide end mills 1, 5, and 9 of the invention.

Additionally, for the purpose of comparison, comparative surface-coatedcemented carbide drills with a single layer structure coating layer(hereinafter referred to as comparative coated cemented carbide drills)were manufactured through the following procedure.

A honing process is performed on the cutting edge of the above cementedcarbide drills 1 to 11. They are also cleaned by ultrasonic cleaning inacetone, and then dried. Thereafter, each drill is placed into the arcion plating apparatus shown in FIG. 2. Under the same conditions asExample 1 aforementioned, the comparative surface-coated cementedcarbide drills 1 to 11 having a hard coating layer was manufactured. Thehard coating layer has a single layer structure with a targetcomposition and a target thickness respectively shown in Table 9.

(c) Next, the performances in drilling of the above coated cementedcarbide drills 1 to 11 of the invention and the above comparative coatedcemented carbide drills 1 to 11 were measured with a condition mentionedin the below (c1), (c2) or (c3).

(c1) For the coated cemented carbide drills 1 to 4 of the invention andfor the comparative coated cemented carbide drills 1 to 4, a cuttingtest, in which these drills try to machine an alloy tool steel for hotdie as a workpiece, was carried out under the following conditions,

Cutting speed: 50 m/min,

Feed: 0.18 mm/rev, and

Hole depth: 10 mm.

Additionally, the workpiece is a plate of JIS-SKD61 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a wet high-speed drilling of alloytool steel for hot die.

(Typical cutting speed of this cutting is 35 m/min.)

(c2) For the coated cemented carbide drills 5 to 8 of the invention andfor the comparative coated cemented carbide drills 5 to 8, a cuttingtest, in which these drills try to machine a chromium-molybdenum steelas a workpiece, was carried out under the following conditions,

Cutting speed: 85 m/min,

Feed: 0.3 mm/rev, and

Hole depth: 20 mm.

Additionally, the workpiece is a plate of JIS-SCM440 with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a wet high-speed drilling ofchromium-molybdenum steel. (Typical cutting speed of this cutting is 60m/min.)

(c3) For the coated cemented carbide drills 9 to 11 of the invention andfor the comparative coated cemented carbide drills 9 to 11, a cuttingtest, in which these drills try to machine a carbon steel for mechanicalstructure as a workpiece, was carried out under the followingconditions,

Cutting speed: 110 m/min,

Feed: 0.3 mm/rev, and

Hole depth: 40 mm.

Additionally, the workpiece is a plate of JIS-S55C with the followingdimensions,

Plane: 100 mm×250 mm and

Thickness: 50 mm.

This cutting test was performed as a wet high-speed drilling of carbonsteel for mechanical structure. (Typical cutting speed of this cuttingis 80 m/min.)

Until the wear width of a flank face at a tip cutting edge face of thesample drill became 0.2 mm, each wet high-speed drilling test mentionedin the above (c1), (c2) or (c3) was performed repeatedly; and then thenumber of holes bored by the sample drill was counted. The test resultsare shown in Tables 8 and 9.

TABLE 8 HARD COATING LAYER UPPER LAYER/THIN LAYER A UNDER LAYER TARGETONE-LAYER TARGET TARGET COMPOSITION TARGET SYMBOL COMPOSITION LAYER(ATOMIC LAYER OF (ATOMIC RATIO) THICKNESS RATIO) THICKNESS TYPE BODY AlCr Ti Si (μm) Al Cr Si (nm) COATED  1 (A) — — — — — 0.35 0.55 0.10 10CEMENTED  2 (A) 0.35 0.55 — 0.10 1 0.35 0.55 0.10 10 CARBIDE  3 (B) 0.45— 0.48 0.07 2 0.45 0.52 0.03 30 DRILL  4 (C) 0.05 — 0.94 0.01 6 0.200.75 0.05 90 OF THE  5 (D) — — — — — 0.42 0.52 0.06 50 INVENTION  6 (D)0.42 0.52 — 0.06 3.5 0.42 0.52 0.06 50  7 (E) 0.15 — 0.80 0.05 5 0.300.65 0.05 50  8 (F) 0.40 0.45 — 0.15 7 0.40 0.45 0.15 70  9 (G) — — — —— 0.45 0.45 0.10 40 10 (G) 0.45 0.45 — 0.10 4 0.45 0.45 0.10 40 11 (H)0.75 — 0.15 0.10 10 0.45 0.40 0.15 100 HARD COATING LAYER UPPER- UPPERLAYER/THIN LAYER B LAYER TARGET ONE-LAYER TOTAL COMPOSITION TARGETTARGET NUMBER (ATOMIC LAYER LAYER OF RATIO) THICKNESS THICKNESS DRILLEDTYPE Al Ti Si (nm) (μm) HOLES COATED  1 0.47 0.50 0.03 20 1 6500CEMENTED  2 0.47 0.50 0.03 20 1 7800 CARBIDE  3 0.45 0.48 0.07 50 5 7500DRILL  4 0.05 0.94 0.01 60 8 6800 OF THE  5 0.50 0.45 0.05 70 1.5 6700INVENTION  6 0.50 0.45 0.05 70 1.5 8000  7 0.15 0.80 0.05 30 3 7300  80.35 0.63 0.02 40 10 7000  9 0.55 0.40 0.05 30 4 2800 10 0.55 0.40 0.0530 4 3200 11 0.75 0.15 0.10 80 5 3000

The compositions of the layers, namely, the under layer and the upperlayer composed of an alternately laminated layer structure of the thinlayers A and B, which constitute the hard coating layer of the coatedcemented carbide drills 1 to 11 of the invention, and the composition ofthe hard coating layer of the comparative coated cemented carbide drills1 to 11 were measured by an energy dispersive X-ray analysis methodusing a transmission electron microscope. The results of thismeasurement show that each layer has a substantially same composition asits target composition respectively. Additionally, the thickness of eachlayer constituting the above hard coating layer was section-measured bythe transmission electron microscope. The results of this measurementshow that each layer has an average thickness (average of five points)which is substantially same thickness as its target thickness.

The results in Tables 8 and 9 show clearly the followings facts.

The hard coating layer of each of the coated cemented carbide drills ofthe invention

-   -   is constituted by the alternately laminated layer of the thin        layer A and the thin layer B, and/or the under layer;    -   has excellent high-temperature hardness and thermoplastic        deformation resistance, and    -   has also excellent high-temperature toughness and        high-temperature strength.

Therefore, even in a drilling performed under the high-speed drillingconditions in which high temperature is generated, and a large impactand/or mechanical load is applied, the hard coating layer can exhibitits excellent wear resistance without the occurrence of chipping orfractures.

On the other hand, if a comparative coated cemented carbide drills, onwhich a hard coating layer composed of an (Al, Cr, Si)N layer (or a hardcoating layer composed of an (Al, Ti, Si)N layer) having a single layerstructure is formed, is used under the above high-speed drillingconditions; such drill's insufficient toughness causes fractures orchipping. Also, such drill's poor wear resistance makes its usable lifetime relatively short period.

INDUSTRIAL APPLICABILITY

The above Examples 1 to 5 clarify the following facts. Thesurface-coated cutting tools of the present invention (for example, thecoated high-speed steel gear cutters of the invention, the coatedcemented carbide end mills of the invention, the coated high-speed steelend mills of the invention, and the coated cemented carbide drills ofthe invention) exhibit excellent fracture resistance and wearresistance, and show excellent cutting performance for a prolongedperiod of time, even if these cutting tools are used in the high-speedgear cutting, high-speed milling, and high-speed drilling in which hightemperature is generated, and a large impact and mechanical load isapplied, as well as in cutting processing under normal cuttingconditions of various kinds of steel or cast iron. Therefore, it ispossible to be sufficiently satisfied with the demand for a highperformance cutting apparatus, labor-saving and energy-saving in cuttingprocess, and cost reduction.

The invention claimed is:
 1. A surface-coated cutting tool comprising ahard coating layer formed on a surface of a tool substrate, the hardcoating layer is composed of an alternately laminated layer structure ofat least a thin layer A and a thin layer B, in which the thin layer Ahas a thickness of 0.01 to 0.1 μm, the thin layer B has a thickness of0.01 to 0.1 μm, and a total thickness of the thin layers A and B iswithin 1 to 10 μm: (a) the thin layer A is a complex nitride layer ofAl, Cr and Si, and when expressing a composition of the complex nitridelayer as a compositional formula [Al_(X)Cr_(Y)Si_(Z)]N, each X, Y and Zsatisfies the relations,0.2≦X≦0.45, 0.4≦Y≦0.75, 0.01≦Z≦0.2, and X+Y+Z=1 (where all of X, Y, andZ are atomic ratios); and (b) the thin layer B is a complex nitridelayer of Al, Ti, and Si, and when expressing a composition of thecomplex nitride layer as a compositional formula [Al_(U)Ti_(V)Si_(W)]N,each U, V and W satisfies the relations,0.05≦U≦0.75, 0.15≦V0.94, 0.01≦W≦0.1, and U+V+W=1 (where all of U, V, andW are atomic ratios), wherein the hard coating layer includes: an upperlayer composed of an alternately laminated layer structure of the thinlayer A and the thin layer B, and an under layer formed so as to beinterposed between the upper layer and the surface of the toolsubstrate; and the under layer has a composition which satisfies thecompositional formula of the thin layer A or the thin layer B.
 2. Thesurface-coated cutting tool according to claim 1, wherein the underlayer has a thickness of 0.5 to 10 μm.
 3. The surface-coated cuttingtool according to claim 1, wherein its hard coating layer includes anupper layer composed of an alternately laminated layer structure of thethin layer A and the thin layer B, and a under layer formed so as to beinterposed between the upper layer and the surface of the toolsubstrate, and the under layer has a thickness of 0.5 to 10 μm, and hasa composition which satisfies the compositional formula of the thinlayer B.
 4. The surface-coated cutting tool according to claim 1,wherein the surface-coated cutting tool is a gear cutter in which itstool substrate is made of a high-speed tool steel.
 5. The surface-coatedcutting tool according to claim 1, wherein the surface-coated cuttingtool is an end mill in which its tool substrate is made of a high-speedtool steel.
 6. The surface-coated cutting tool according to claim 1,wherein the surface-coated cutting tool is an end mill or a drill inwhich its tool substrate is made of tungsten-carbide-based cementedcarbide.
 7. The surface-coated cutting tool according to claim 2,wherein the surface-coated cutting tool is a gear cutter in which itstool substrate is made of a high-speed tool steel.
 8. The surface-coatedcutting tool according to claim 3, wherein the surface-coated cuttingtool is a gear cutter in which its tool substrate is made of ahigh-speed tool steel.
 9. The surface-coated cutting tool according toclaim 2, wherein the surface-coated cutting tool is an end mill in whichits tool substrate is made of a high-speed tool steel.
 10. Thesurface-coated cutting tool according to claim 3, wherein thesurface-coated cutting tool is an end mill in which its tool substrateis made of a high-speed tool steel.
 11. The surface-coated cutting toolaccording to claim 2, wherein the surface-coated cutting tool is an endmill or a drill in which its tool substrate is made oftungsten-carbide-based cemented carbide.
 12. The surface-coated cuttingtool according to claim 3, wherein the surface-coated cutting tool is anend mill or a drill in which its tool substrate is made oftungsten-carbide-based cemented carbide.